Piston and retaining assemblies for a radial piston pump or motor

ABSTRACT

An improved radial piston pump or motor of the type wherein a rotor is rotatably mounted upon a pintle valve spindle eccentrically fixed within a cylindrical race, the rotor having hollow radial spokes communicated with passages of the pintle valve and reciprocably mounting hollow pistons thereon having shoes riding against the inside of the race. Each piston is of unique two-part construction preferably including a bronze shoe such that the race against which it rides may be advantageously of steel. In addition, the shoe of each piston is preferably provided with a flange which rides upon retaining protrusions of the race.

United States Patent 1191 Engel PISTON AND RETAINING ASSEMBLIES FOR ARADIAL PISTON PUMP OR MOTOR [75] Inventor: William K. Engel, Peoria,111.

[73] Assignee: Caterpillar Tractor Co., Peoria, 111.

[22] Filed: June 1, 1971 [21] App]. No.: 148,779

[52] US. Cl. 91/490, 91/491 [51] Int. Cl. F0lb l/l00, FOlb 13/04 [58]Field of Search 91/490, 491, 498;

123/193 C, 193 CH, 44 E; 418/179 [56] References Cited UNITED STATESPATENTS 3,530,768 9/1970 Engel ..-91/491 3,036,557 5/1962 Kimsey.9l/490X FOREIGN PATENTS OR APPLICATIONS 1,254,200 1/1961 France 91/4981451 July 3,1973

971,521 1 1951 France 91 491 Primary Examiner-Charles .1. MyhreAssistant Examiner-Frank H. McKenzie, Jr. Attorney-Fryer, Tjensvold,Feix, Phillips & Lempio [57] ABSTRACT An improved radial piston pump ormotor of the type wherein a rotor is rotatably mounted upon a pintlevalve spindle eccentrically fixed within a cylindrical race, the rotorhaving hollow radial spokes communicated with passages of the pintlevalve and reciprocably mounting hollow pistons thereon having shoesriding against the inside of the race. Each piston is of unique two-partconstruction preferably including a bronze shoe such that the raceagainst which it rides may be advantageously of steel. In addition, theshoe of each piston is preferably provided with a flange which ridesupon retaining protrusions of the race.

5 Claims, 1 Drawing Figure PATENTEDJULS ma Q 3. 742.818

INVENTOR WILLIAM K. ENGEL ATTORNEYS PISTON AND RETAINING ASSEMBLIES FORA RADIAL PISTON PUMP OR MOTOR BACKGROUND 'OF THE INVENTION Radial pistonpumps or motors are variously employed in hydrostatic applications forconverting mechanical torque to hydraulic pressure or hydraulic pressureto mechanical torque. Such a power transfer device is disclosed, forexample, in U.S. Pat. No. 3,274,946 which issued Sept. 27, 1966 to E. E.Simmons.

Briefly, the device includes a pintle valve spindle coaxially mounted infixed position within a housing, and a cylindrical race fixedly mountedtherein eccentrically about the spindle. A rotor is rotatably receivedupon the spindle and provided with a plurality of circumferentiallyspaced spokes projecting radially therefrom. The spokes are hollow so asto define radial passages which are arranged to communicate with valvepassages of the spindle during rotation of the rotor thereon.

The outer end of each spoke is provided with an annular sphericalbearing member which serves to mount a hollow cylindrical piston forreciprocation thereon, the interior of the piston communicating with thepassage of the spoke. The head end of each piston isformed as a shoewhich rides against the inside of the race during rotor rotation. Fordetails as to the operation of such a device, reference may be had tothe previously referenced patent.

In a power transfer device of the class outlined above, it has been theusual practice to fabricate the race from a material such as bronze andto integrally fabricate each piston from a material such as steel. Thishas not resulted in a particularly compatible running relationshipbetween the piston shoes and race which has thereby limited the life ofthe parts and detracted from trouble-free service of the device. Becauseof the one-piece construction of the piston it has been relativelydifficult to machine the inner diameter of the skirt portion thereofwith accuracy. Further, the onepiece construction of the piston issusceptible to nonuniform flexing of its skirt portion which detractsfrom the uniformity of clearance that can be maintained between theskirt interior and bearing portion of a spoke and thereby limits controlof oil leakage therebetween.

In addition, with a great number of conventional radial piston powertransfer designs, means are not provided to positively retain thepistons in close proximity to the inside control surface of the race toprevent the pistons from banging into the surface during initial startupof the device.

SUMMARY OF THE INVENTION The present invention relates to a radialpiston power transfer device for use as a hydrostatic pump or motorwhich is characterized by improved piston and retaining assemblies.portion It is a general object of the present invention to provide adevice of the class described having improved troublefree service.

Another object of the invention is the provision of an improved pistonassembly for a radial piston power transfer device which is arranged toprovide a more compatible longer life running relationship between theshoe portion of the piston and control surface of the race.

It is yet another object of the present invention to provide a two-partpiston assembly for a radial piston power transfer device, which willfacilitates easy accurate machining of the inner diameter of the skirtportion of the piston and uniform flexing thereof throughout its lengthin order to afford improved leakage control of oil between the pistonand spoke bearing of the rotor of the device.

A further object of the invention is the provision of a piston assemblyof the class described having a flanged head shoe portion for ridingupon retaining protrusions of the race to maintain the shoe portion inintimate contact with the control surface of the race such that duringstartup of the device hanging of the piston assembly into the controlsurface of the race (due to centrifugal forces or the onset of hydraulicpressure) is prevented.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a sectional viewthrough an improved radial piston power transfer device in accordancewith the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTIONReferring now to the drawing in detail, there is shown a radial pistonhydrostatic power transfer device 11 which may be employed as a pump ormotor to convert mechanical torque to hydraulic pressure or hydraulicpressure to mechanical torque. In basic respects the device is similarto that disclosed in the previously referenced U. S. Pat. No. 3,274,946,and therefore the device ll is only described hereinafter to the extentnecessary to facilitate a full understanding of the salient aspects ofthe present invention.

The power transfer device 11 includes a rotor assembly 12 rotated aboutand carried in intimate contact with a pintle valve spindle l3 fixedlysecured as by means of cap screws 14 to one end cover 16 of a generallycylindrical housing assembly 17, preferably in coaxial relation thereto.The complete housing assembly is preferably formed by the end cover 16,an opposed end cover 18, and an interposed cylindrical portion 19 boltedtherebetwen.

The rotor assembly 12 comprises a cylindrical hub 21 rotatablyconcentrically mounted upon the spindle l3 and axially positioned andretained as by means of thrust washers 22 and 23 respectively interposedbetween one end face of the hub and a shoulder of the spindle andbetween the opposite end face of the hub and the housing cover 18.

A plurality of circumferentially spaced spokes 24 are secured to thehub, as by welding, to project radially outward therefrom, such spokesbeing hollowto define radial passages 26 in registry with apertures 27through the hub in communication with passages 28 of the pintle valvespindle 13 during rotation of the rotor assembly thereon. On the outerend of each spoke 24 there is secured an annular spherical bearingmember 29 which serves to mount a hollow piston assembly 31, inaccordance with the present invention, for reciprocation thereon.

The h'ead'ends of the piston assemblies ride against a cylindricalcontrol surface of a race 32 mounted within housing assembly 17eccentrically about the rotorassembly 12 which thereby serves toreciprocate the pistons upon the spokes during rotation of the rotorupon the pintle valve spindle.

Considering now the particularly salient aspects of the presentinvention, it is to be noted that heretofore it has been the practice tofabricate the race 32 from a material such as bronze, and to integrallyfabricate each piston as a single part from a material such as steel.This has not resulted in a particularly compatible running relationshipbetween the pistons and the race in that the bronze race is excessivelysusceptible to denting and scuffing by the radially reciprocating steelpistons.

Moreover, with a one-part piston it is relatively difficult toaccurately machine the inner diameter of the skirt portion thereof forclose fitting reciprocating engagement with the bearing members 29 ofthe spokes 24. Furthermore, a one-part piston gives rise to nonuniformflexing along the length of the skirt portion which thereby detractsfrom the uniformity of clearance and control of oil leakage that can bemaintained between the inner diameter of the skirt portion and the spokebearing member.

Accordingly, in accordance with the improvements of the presentinvention each piston assembly 31 is of novel two-part constructionincluding a hollow cylindrical skirt portion 33 and a separate shoe 34sealably secured to one end of the skirt portion to define the head endof the piston which rides against the control surface of the race 32.

Sealed securance betwen the parts is preferably facilitated by formingthe shoe 34 with a depending annular flange 36 having an outwardlyflared lip at its end, and an annular groove 37 circumscribing theflange and radially inwardly undercut at its base. The skirt portion 33is formed at one end with a complementary coaxially projecting annularflange 38 with an inwardly flared lip at its end, and an undercutannular shoulder 39 inwardly of the flange.

The shoe flange 36 conformably engages the undercut shoulder 39 of theskirt portion and the skirt flange 38 conformably engages the shoegroove 37 to provide a sealed joint between the parts. It isparticularly important to note that the shoe 34 is ofa material such asbronze while the race 32 is of a material such as steel. The runningrelationship between the bronze capped piston assemblies 31 and steelrace 32 has improved compatibility and provides relatively trouble-freeservice.

Of course, by virtue of the skirt portion 33 being a separatecylindrical part, its inner diameter may be accurately machined withrelative ease. The sealed joint between the shoe 34 and skirt portin 33permits uniform flexing of the latter throughout its length withoutdisruption of the seal.

As another important feature of the invention, the shoe 34 preferablyextends radially outward beyond the outer periphery of the skirt portion33 to define an outwardly flared annular flange 41. Such flange ridesagainst protrusions 42 of the race 32 which serve to positively radiallyretain the piston shoes 34 in intimate contact with the control surfaceof the race to prevent centrifugal hanging of the shoes against the raceduring startup of the power transfer device 11.

More particularly, the race 32 is preferably of a U- shaped crosssection formed of a control surface defin ing ring 43 and a pair ofcoaxially spaced annular covers 44 secured to the opposite ends of thering to extend radially inward therefrom. The retaining protrusions 42are then provided as annular lips which project coaxially inward fromthe inner faces of the covers 44 in radially inwardly spaced relation tothe inner control surface of the ring 43 of the race 32. The grooves 46thereby defined between the protrusions 42 and inner surface of ring 43serve to receive the flange 41 of each piston assembly 31 such that theshoe 34 thereof is radially retained in intimate contact with thecontrol surface of the race.

Although the invention has been hereinbefore described and illustratedin the accompanying drawing with respect to a single preferredembodiment, it wild be appreciated that numerous modifications andchanges may be made therein without departing from the true spirit andscope of the invention, and thus it is not intended to limit theinvention except by the terms of the appended claims.

What is claimed is:

1. In a radial piston hydrostatic power transfer device of the typeincluding a pintle valve spinlder flxedly secured within a housing, arotor rotatably mounted upon the spindle and having a plurality ofcircumferentially spaced radially projecting spokes with radial passagescommunicating with passages of the pintle valve spindle, each spokehaving an annular spherical bearing member at its outer end, and anannular race fixedly secured within the housing eccentrically about therotor, the improvement comprising a plurality of two-part pistonassemblies reciprocagly mounted upon said spokes, each of said pistonassemblies having a hollow cylindrical skirt portion with an innersurface in bearing relation to the bearing member of one of said spokesand a separate shoe sealably secured to an end of said skirt portion andengaging a cylindrical control surface of said race, further defined bysaid shoe of each of said piston assemblies having a depending annularflange having an outwardly flared lip at its end and an annular groovecircumscribing said flange and radially inwardly undercut at its base,said skirt portion of each of said piston assemblies having ancomplementary coaxially projecting annular flange with an inwardlyflared lip at its end and an undercut annular shoulder inwardly thereof,said flange of said shoe conformably engaging said shoulder of saidskirt portion and said flange of said skirt portion conformably engagingsaid groove of said shoe.

2. The combination of claim 1, further defined by said shoe of each ofsaid piston assemblies being of bronze and said race being of steel.

3. In a radial piston hydrostatic power transfer device of the typeincluding a pintle valve spindle fixedly secured within a housing, arotor rotatably mounted upon the spindle and having a plurality ofcircumferentially spaced radially projecting spokes with radial passagescommunicating with passages of the pintle valve spindle, each spokehaving an annular spherical bearing member at its outer end, and anannular race fixedly secured within the housing eccentrically about therotor, the improvement comprising a plurality of two-part pistonassemblies reciprocably mounted upon said spokes, each of said pistonassemblies having a hollow cylindrical skirt portion with an innersurface in bearing relation to the bearing member of one of said spokesand a separate shoe sealably secured to an end of said skirt portion andengaging a cylindrical control surface of said race, further defined byretaining means positively radially retaining said shoes of said pistonassemblies in intimate Contact with said control surface of said race,further defined by said shoe of each piston assembly extending radiallybeyond the outer periphery of said skirt portion thereof to define anoutwardly flared annular flange, said race having annular protrusions inradially spaced relation to said control surface of said race definingannular retaining grooves between said protrusions and said controlsurface, said outwardly flared flanges of said piston assembliesengaging said retaining grooves.

4. The combination of claim 3, further defined by said shoe of each ofsaid piston assemblies having a depending annular flange having anoutwardly flared lip bronze and said race being of steel.

1. In a radial piston hydrostatic power transfer device of the typeincluding a pintle valve spindle fixedly secured witHin a housing, arotor rotatably mounted upon the spindle and having a plurality ofcircumferentially spaced radially projecting spokes with radial passagescommunicating with passages of the pintle valve spindle, each spokehaving an annular spherical bearing member at its outer end, and anannular race fixedly secured within the housing eccentrically about therotor, the improvement comprising a plurality of two-part pistonassemblies reciprocably mounted upon said spokes, each of said pistonassemblies having a hollow cylindrical skirt portion with an innersurface in bearing relation to the bearing member of one of said spokesand a separate shoe sealably secured to an end of said skirt portion andengaging a cylindrical control surface of said race, further defined bysaid shoe of each of said piston assemblies having a depending annularflange having an outwardly flared lip at its end and an annular groovecircumscribing said flange and radially inwardly undercut at its base,said skirt portion of each of said piston assemblies having acomplementary coaxially projecting annular flange with an inwardlyflared lip at its end and an undercut annular shoulder inwardly thereof,said flange of said shoe conformably engaging said shoulder of saidskirt portion and said flange of said skirt portion conformably engagingsaid groove of said shoe.
 2. The combination of claim 1, further definedby said shoe of each of said piston assemblies being of bronze and saidrace being of steel.
 3. In a radial piston hydrostatic power transferdevice of the type including a pintle valve spindle fixedly securedwithin a housing, a rotor rotatably mounted upon the spindle and havinga plurality of circumferentially spaced radially projecting spokes withradial passages communicating with passages of the pintle valve spindle,each spoke having an annular spherical bearing member at its outer end,and an annular race fixedly secured within the housing eccentricallyabout the rotor, the improvement comprising a plurality of two-partpiston assemblies reciprocably mounted upon said spokes, each of saidpiston assemblies having a hollow cylindrical skirt portion with aninner surface in bearing relation to the bearing member of one of saidspokes and a separate shoe sealably secured to an end of said skirtportion and engaging a cylindrical control surface of said race, furtherdefined by retaining means positively radially retaining said shoes ofsaid piston assemblies in intimate contact with said control surface ofsaid race, further defined by said shoe of each piston assemblyextending radially beyond the outer periphery of said skirt portionthereof to define an outwardly flared annular flange, said race havingannular protrusions in radially spaced relation to said control surfaceof said race defining annular retaining grooves between said protrusionsand said control surface, said outwardly flared flanges of said pistonassemblies engaging said retaining grooves.
 4. The combination of claim3, further defined by said shoe of each of said piston assemblies havinga depending annular flange having an outwardly flared lip at its end andan annular groove circumscribing said flange and radially inwardlyundercut at its base, said skirt portion of each of said pistonassemblies having a complementary coaxially projecting annular flangewith an inwardly flared lip at its end and an undercut annular shoulderinwardly thereof, said flange of said shoe conformably engaging saidshoulder of said skirt portion and said flange of said skirt portionconformably engaging said groove of said shoe.
 5. The combination ofclaim 4, further defined by said shoe of each of said piston assembliesbeing of bronze and said race being of steel.